During cardiac surgery, the function of the heart and lungs is replaced by an external pump due to the difficulty of operating on a beating heart. This technique, called cardiopulmonary bypass (CPB), maintains circulation of blood and oxygen in the patient's body. Retransfusion is attractive because it reduces the need for allogeneic transfusion, minimizes costs, and decreases transfusion-related morbidity. Heterologous transfusions are also linked to increased long term mortality after cardiac surgery.
However, when layers of fat are cut during surgery, they release lipids that can be collected by the pump during suctioning. These lipids are then unintentionally introduced to the bloodstream when blood is re-transfused to the body. The lipids can cause lipid microemboli, in which the emulsified (in suspension) fat cells travel to the patient's organs (e.g. kidney, lung, heart) and can cause blockage of blood vessels (embolization). This is especially dangerous when lipid micro-emboli occur in the brain, as they can cause various neuro-cognitive disorders. More than 50% of patients experience neurological deficits in the first week after CPB, 10-30% have long term or permanent affects, and 1-5% experience permanent disability or death.
Existing methods for removing lipids from blood, such as filtering and centrifugation, are either inefficient or harmful to the beneficial red blood cells in the flood. Lipid particles show a size distribution of approximately 5-70 micrometers (μm) in diameter, with most particles being ≤10 μm. This is about the same size as red blood cells. Typical filters have a pore size of 25-40 μm, and a lipid removal efficiency of 30-40%. Also, filters clog and suffer from throughput constraints, need replacement, and may disperse larger droplets into smaller droplets. Centrifugation is time-consuming, expensive, and requires trained personnel. Also, the high speeds required for centrifugation may damage the blood cells, and removes beneficial blood components such as platelets and clotting factors. Some MEMS devices have been used, but rely on very small passages that essentially “line up” red blood cells and lipid particles for separation. This results in very low throughput, and cannot handle large amounts in bulk.
There is a need for a separation technology that can efficiently and adequately remove lipids from blood.